Posted
by
samzenpuson Monday January 06, 2014 @12:10AM
from the there's-a-first-time-for-everything dept.

sciencehabit writes "In a cosmic coup, astronomers have found a celestial beacon known as a pulsar in orbit with not one, but two other stars. The first-of-its-kind trio could soon be used to put Einstein's theory of gravity, or general relativity, to an unprecedented test. 'It's a wonderful laboratory that nature has given us,' says Paulo Freire, a radio astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, who was not involved in the work. 'It's almost made to order.'"

Meh, just simulate it. No need to solve the equations, and simulating it isn't very hard. We have computers now, they are good at this.

But how do you know if your simulation is correct?

Anyone could easily write a sim that has three stars and they all coexist, happily passing through each other or something ridiculous. The point here is that we can see if the Theory and any simulations match the real world.

It's just a bloody simple system of differential equations. n bodies, each has a location (3 coordinates) and a speed vector (3 coordinates), so you have six equations. The speed is obviously the derivative of the location, and the theory gives you the equation to calculate the derivative of the speed. Look up Fehlberg or "Adaptive Runge-Kutta-Fehlberg" and you are there.

That's Newton.

With relativity things get hard, quick. Both time (thus, speed) and space (thus, speed and distance) dilate, mass changes (thus, the attractive forces between bodies and thus their acceleration, and thus their speed, and thus their location), and some other oddities.